I suppose the question is whether or not pon farr is a purely biological drive, or if it has psychological components to it. At the time of "Amok Time," Spock was trying very hard to deny his human half, repress all emotions, and function as a 100% Vulcan. And McCoy himself speculated that the madness of pon farr might be the price they pay for repressing their emotions the rest of the time.

By the time we get to the movies, particularly by the end of TMP, Spock is much more comfortable in his own skin. He's learned to accept both his Vulcan and human halves. And he's seemingly come to realize the importance of accepting his human emotions, even if he doesn't display them outwardly. He admits friendship for Kirk openly where before in "The Naked Time" he claimed he was ashamed to feel friendship. He tells Sarek to tell Amanda he feels fine. And he tells Valeris that "logic is the beginning of wisdom... not the end."

Perhaps the fact that Spock actually came to terms with the need for both sides of himself has allowed him to be free of the madness of pon farr that other Vulcans are forced to live with.